repository: introduce register_changeset callback

The new callback is called whenever a changeset is added to the repository
(commit, unbundle or exchange). Since the bulk operations already parse
the changeset (readfiles or full changesetrevision), always use the
latter to avoid redundant lookups. The first consumer of the new
interface needs to look at extra.

Differential Revision: https://phab.mercurial-scm.org/D9780

mercurial/changegroup.py

@@ -323,7 +323,10 b' class cg1unpacker(object):'
                     cgnodes.append(node)
 
             def onchangelog(cl, node):
-                efilesset.update(cl.readfiles(node))
+                rev = cl.rev(node)
+                ctx = cl.changelogrevision(rev)
+                efilesset.update(ctx.files)
+                repo.register_changeset(rev, ctx)
 
             self.changelogheader()
             deltas = self.deltaiter()

mercurial/commit.py

@@ -97,6 +97,9 b' def commitctx(repo, ctx, error=False, or'
             extra,
         )
         rev = repo[n].rev()
+        if oldtip != repo.changelog.tiprev():
+            repo.register_changeset(rev, repo.changelog.changelogrevision(rev))
+
         xp1, xp2 = p1.hex(), p2 and p2.hex() or b''
         repo.hook(
             b'pretxncommit',

mercurial/exchangev2.py

@@ -372,6 +372,8 b' def _processchangesetdata(repo, tr, objs'
         # so we can set the linkrev accordingly when manifests are added.
         manifestnodes[rev] = revision.manifest
 
+        repo.register_changeset(rev, revision)
+
     nodesbyphase = {phase: set() for phase in phases.phasenames.values()}
     remotebookmarks = {}
 

mercurial/interfaces/repository.py

@@ -1641,6 +1641,14 b' class ilocalrepositorymain(interfaceutil'
     def revbranchcache():
         pass
 
+    def register_changeset(rev, changelogrevision):
+        """Extension point for caches for new nodes.
+
+        Multiple consumers are expected to need parts of the changelogrevision,
+        so it is provided as optimization to avoid duplicate lookups. A simple
+        cache would be fragile when other revisions are accessed, too."""
+        pass
+
     def branchtip(branchtip, ignoremissing=False):
         """Return the tip node for a given branch."""
 

mercurial/localrepo.py

@@ -2062,6 +2062,9 b' class localrepository(object):'
             self._revbranchcache = branchmap.revbranchcache(self.unfiltered())
         return self._revbranchcache
 
+    def register_changeset(self, rev, changelogrevision):
+        pass
+
     def branchtip(self, branch, ignoremissing=False):
         """return the tip node for a given branch